Residual stress generated in a structure causes damage such as fatigue cracks in some cases and it is important to accurately grasp the distribution of the residual stress in the structure. As a method of estimating the residual stress of a structure, there has been known a method using an inherent strain method (for example, refer to Patent Documents 1 and 2).
In the method of estimating residual stress based on the inherent strain method of the related art, two kinds of cut pieces are cut out from a structure, the elastic strain or residual stress of each cut piece measured is measured, and the measured value of the elastic strain or residual stress of each cut piece is applied to inverse analysis processing based on a finite element method. In the inverse analysis processing, inherent strain is approximated with a least squares method using a distribution function and a distribution of inherent strain in the structure is determined, thereby calculating the residual strain of the structure before cutting from the obtained inherent strain distribution.
Patent Document 1 discloses that cut pieces of a T piece and an L piece are cut out from a test piece of a structure, and the respective T piece and L piece are further cut and divided into a plurality of small pieces to measure elastic (released) strain.